What must a scientist determine from blood stains in a CSI?

What must a scientist determine from blood stains in a CSI?

Richard Saferstein (Former Chief Forensic Scientist) gives expert video advice on: What is blood made of?; How does the classification of blood type help in CSI?; Why are blood stains studied in CSI? and more...

The first thing that we have to do when we examine a blood stain is to make a determination as to whether it is indeed blood, as opposed to ketchup or some other material that may look like blood. Typically, we'll use a color test known as the Castlemeyer color test, to answer that question. However, in some crime scenes, it's just very difficult to find these things. The blood may have been cleaned up thoroughly or there may be just a few specks that are hard to see with the human eye. We use a test known as the luminal test, which is a test that is very sensitive for blood, in order to ascertain whether there are any trace amounts of blood that may be present at a crime scene. Essentially, the luminal test involves spraying a suspect area, darkening the room, and looking for a glow or the emanation of light from the suspect stain. If that occurs, then there's a good chance that we are dealing with blood. If we do have blood, we now have to determine the species of the blood. Is it human, or animal? Here, we rely upon commercial anti-serum. There are companies that forensic scientists can purchase anti-serum related to various animals such as deer, cats, or dogs. Serological tests will be carried out in the laboratory in order to ascertain whether a blood stain emanated from a human or from some other animal using this anti-serum that is commercially available. Finally, once we ascertain that the blood emanated from a human being, then we undertake DNA testing.